For the first time in history, the middle-aged make up the largest, richest and most influential segment in the country, says New York Times reporter Patricia Cohen. A trillion-dollar economy has grown up feeding and fueling their needs, whims, and desires, while millions of federal and foundation dollars have been spent on scientific research into their habits, health, marriages, divorces, fears, and passions. Cohen's book is a biography of the idea of middle age from its invention in the late 19th century, in which she traces the various definitions of middle age in biological, psychological, and sociological terms. She also dismantles some of the most stubborn myths about the middle years, from the midlife crisis to the empty nest syndrome.